1. Technical Field
The disclosure relates to a data processing circuit and a signal generation method. Particularly, the disclosure relates to a clock data recovery circuit module and a method for generating data recovery clock.
2. Related Art
Generally, a clock data recovery circuit is configured at a signal receiving end of a data transmission interface to recover a received input signal according to a data recovery clock, so as to generate a retimed data stream. In some specific specifications, to ensure accuracy of data recovered by the clock data recovery circuit, jitter of the retimed data stream cannot be too large. Therefore, at the signal receiving end, an oscillator used in collaboration with a phase-locked loop is generally a crystal oscillator, so as to satisfy the demand for accuracy. An error between a frequency of a reference clock generated by the crystal oscillator and a frequency of the input signal has to be within a certain range. Taking a universal serial bus 3.0 (USB 3.0) specification as an example, the error between the frequency of the reference clock and the frequency of the input signal has to be smaller than 300 ppm (parts per million). Although the commercial crystal oscillator can generate the clock signal with the frequency error lower than ±100 ppm to serve as an ideal clock signal source, the price of the crystal oscillator is expansive, and the crystal oscillator occupies a larger circuit board space.
In order to save the cost and the circuit board space, according to a conventional technique, a high accuracy reference clock is provided to the phase-locked loop according to a method of auto-tracking data recovery clock frequency. However, according to such method, in a process that the USB establishes a communication link, or under a low power mode operation, if the data recovery clock is continuously tracked, accuracy of the frequency of the reference clock is decreased.
Nothing herein should be construed as an admission of knowledge in the prior art of any portion of the present invention. Furthermore, citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention, or that any reference forms a part of the common general knowledge in the art.